Role of biological control agents and physical treatments in maintaining the quality of fresh and minimally-processed fruit and vegetables

Temperature-driven divergence in molecular distribution and microbial invasion and the associated texture softening during dual-phase fermentation of Paocai

Temperature is an important driving force that shapes the texture of fermented vegetables through driving the molecular distribution and microbial invasion between the liquid phase (brine) and the solid phase (vegetables) during fermentation. The objective of this study was to investigate the texture softening by investigating firmness, microstructure, physicochemical properties, molecular distribution and microbial community between brine and vegetables of Paocai as affected by fermentation temperatures of 10 °C, 20 °C and 30 °C. Results demonstrated that, compared with 10 °C and 30 °C, 20 °C attenuated softening of Paocai by restraining microbial invasion and suppressing pectinolysis. Moreover, at 20 °C, a balanced molecular distribution and microbial community were achieved between vegetables and brine, thus accomplishing acid-production fermentation. By contrast, 10 °C and 30 °C promoted nonfermentative microbial genera, retarding fermentation. This study provided an understanding of the divergent influence of temperature on quality formation of fermented vegetables during fermentation.

Research on the Isolation of Endophytic Fungi from Papaya and the Prevention of Colletotrichum gloeosporioides

Endophytic fungi can be used as a source of herbal antioxidants to overcome the limitations of low yield and lengthy growth cycles associated with using plants as raw materials for antioxidant production. Papaya fruit is often susceptible to infection by Colletotrichum gloeosporioides after harvest, leading to postharvest rot. Endophytic fungi were extracted with ethyl acetate, and the initial screening concentration was 100 mg/L. Seven strains were identified, with scavenging rates exceeding 50% and strong antioxidant activity. The IC50 values in DPPH and ABTS free radical scavenging assays ranged from 19.72 to 84.06 mg/L and from 14.34 to 64.63 mg/L, respectively. Strain Y17 exhibited robust antioxidant activity (IC50 < 20 mg/L) and was identified as Penicillium rolfsii (MT729953) through ITS sequencing. Treatment of papaya fruit wounds with a fermentation broth of strain Y17 significantly inhibited the infection and colonization of anthracnose pathogens, resulting in a slowed disease incidence rate. This promoted the activity of protective enzymes, such as CAT, POD, and SOD, in the papaya fruit and slowed down the rate of MDA accumulation. This strain, which was found to have antioxidant activity in this study, has the potential to control anthracnose in papaya and has value in terms of further development and utilization.

Exploring the Antimicrobial Efficacy of Low-Cost Commercial Disinfectants Utilized in the Agro-Food Industry Wash Tanks: Towards Enhanced Hygiene Practices

The increase in vegetable consumption has underlined the importance of minimizing the risks associated with microbiological contamination of fresh produce. The critical stage of the vegetable washing process has proven to be a key point for cross-contamination and the persistence of pathogens. In this context, the agri-food industry has widely adopted the use of disinfectants to reduce the bacterial load in the wash water. Therefore, we conducted laboratory-scale experiments in order to demonstrate the antimicrobial activity of disinfectants used in the wash tank of agro-food industries. Different wash water matrices of shredded lettuce, shredded cabbage, diced onion, and baby spinach were treated with sodium hypochlorite (NaClO), chlorine dioxide (ClO2), and per-oxyacetic acid (PAA) at recommended concentrations. To simulate the presence of pathogenic bacteria, a cocktail of E. coli O157:H7 was inoculated into the process water samples (PWW) to determine whether concentrations of disinfectants inhibit the pathogen or bring it to a viable non-culturable state (VBNC). Hereby, we used quantitative qPCR combined with different photo-reactive dyes such as ethidium monoazide (EMA) and propidium monoazide (PMA). The results indicated that concentrations superior to 20 ppm NaClO inhibit the pathogen E. coli O157:H7 artificially inoculated in the process water. Concentrations between 10-20 ppm ClO2 fail to induce the pathogen to the VBNC state. At concentrations of 80 ppm PAA, levels of culturable bacteria and VBNC of E. coli O157:H7 were detected in all PWWs regardless of the matrix. Subsequently, this indicates that the recommended concentrations of ClO2 and PAA for use in the fresh produce industry wash tank do not inhibit the levels of E. coli O157:H7 present in the wash water.

Health Benefits of High Voltage Electrostatic Field Processing of Fruits and Vegetables

High voltage electrostatic field processing (HVEF) is a food preservation procedure frequently used to produce healthy minimally processed fruits and vegetables (F&V) as it reduces the growth of microorganisms and activates or inhibits various enzymes, thus retarding their natural ripening while preserving and even enhancing native nutritional quality and sensory characteristics. HVEF is one of the various nonthermal processing technology (NTPT) regarded as abiotic stress that can activate the antioxidant system of F&V and can also inhibith spoilage enzymes as, polyphenol oxidase (PPO), lipoxygenase (LOX), pectin methylesterase (PME), polygalacturonase (PG), cellulase (Cel), β-xylosidase, xyloglucan and endotransglycosylase/hydrolase, bringing positive effect on hardness, firmness, colour attributes, electric conductivity, antioxidant compounds, microstructure and decreasing electrolyte leakage (EL), malondialdehyde (MDA) contents and browning degree. This technique can also increase the contents of fructose, glucose, and sucrose and decrease the production of CO2 and H2O2. Additionally, it has been reported that HVEF could be used with other treatments, such as modified atmosphere packaging (MAP) and acidic electrolyzed water (AEW) treatment, to enhance its effects. Future works should deepen on elucidating the activation of the antioxidant systems by applying HVEF of critical enzymes related to the synthesis pathways of phenolic compounds (PC) and carotenoids (Car). Holistic approaches to the effects of HVEF on metabolism based on systems biology also need to be studied by considering the overall biochemical, physical, and process engineering related aspects of this technique.

Endophytic Fungi Volatile Organic Compounds as Crucial Biocontrol Agents Used for Controlling Fruit and Vegetable Postharvest Diseases

Fruits and vegetables are an important part of the human diet, but during transportation and storage, microbial pathogens attack and spoil fruits and vegetables, causing huge economic losses to agriculture. Traditionally used chemical fungicides leave chemical residues, leading to environmental pollution and health risks. With the emphasis on food safety, biocontrol agents are attracting more and more attention due to their environmental friendliness. Endophytic fungi are present in plant tissues and do not cause host disease. The volatile organic compounds (VOCs) they produce are used to control postharvest diseases due to their significant antifungal activity, as well as their volatility, safety and environmental protection characteristics. This review provides the concept and characterization of endophytic fungal VOCs, concludes the types of endophytic fungi that release antifungal VOCs and their biological control mechanisms, as well as focuses on the practical applications and the challenges of applying VOCs as fumigants. Endophytic fungal VOCs can be used as emerging biocontrol resources to control postharvest diseases that affect fruits and vegetables.

Improving fresh-cut fruit salad quality and longevity with chitosan coating enriched with poppy seed phenolics

This innovative study introduces the application of a 5% (v/v) poppy seed phenolic extract-infused edible chitosan coating on fresh-cut fruit salads (comprising apple, pineapple, pomegranate, and kiwi) stored at +4°C for 12 days. Non-coated samples experienced notable changes: 4.30% weight loss, 25% decay, pH level at 3.59, titratable acidity of 0.18%, and browning index of 1.71. In contrast, fruit salads coated with chitosan-poppy seed phenolic extract exhibited significant improvements: weight loss reduced to 3.10%, decay limited to 3.13%, pH increased to 3.76, titratable acidity enhanced to 0.20%, and browning index notably decreased to 0.33. Soluble solids ranged from 11.83 to 14.71, L* from -8.13 to 18.64, a* from -1.85 to 22.35, and b* from 8.26 to 27.89 in non-coated salads. Adding poppy seed phenolic extract to the coated fruits slightly expanded these ranges. Sensory evaluations consistently rated non-coated samples between 1 and 3, while the coated samples received higher ratings between 6 and 7. These assessments consistently highlighted enhanced attributes, including intensified aroma, enriched color, improved taste, texture, and overall acceptability. Moreover, incorporating poppy seed phenolic extract amplified sensory qualities and significantly improved microbial safety (<106 CFU/g). In summary, the chitosan-based coating, enriched with poppy seed phenolic extract, effectively extended the shelf life of fresh-cut fruit salads. This integrated approach preserves key attributes, ensures microbial quality, and enhances the sensory characteristics of these products. The study's results emphasize its potential as a pivotal innovation in food preservation by providing specific and tangible outcomes.

Predicting the effect of chemicals on fruit using graph neural networks

The neural network method is a type of machine learning that has made significant advances over the past few years in a variety of fields, particularly text, speech, images, videos, etc. In areas where data is unstructured, traditional machine learning has not been able to surpass the 'glass ceiling'; therefore, researchers have turned to neural networks as auxiliary tools to achieve significant breakthroughs or develop new research methods. An array of computational chemistry challenges can be addressed using neural networks, including virtual screening, quantitative structure-activity relationships, protein structure prediction, materials design, quantum chemistry, and property prediction, among others. This paper proposes a strategy for predicting the chemical properties of fruits by using graph neural networks, and it aims to provide some guidance to researchers and streamline the identification process.

On the Way to the Technological Development of Newly Selected Non-Saccharomyces Yeasts Selected as Innovative Biocontrol Agents in Table Grapes

Post-harvest decay of fresh table grapes causes considerable annual production losses. The main fungal agents of decay both in pre- and post-harvest are B. cinerea, Penicillium spp., Aspergillus spp., Alternaria spp., and Cladosporium spp. To date, the use of agrochemicals and SO2 are the main methods to control grape molds in pre- and postharvest, respectively. Significant improvements, however, have already been made in to apply innovative and more environmentally sustainable control strategies, such as Biological Control Agents (BCAs), which can reduce disease severity in both pre- and post-harvest. In this study, 31 new non-Saccharomyces yeast strains, isolated from berries of native Apulian table grape genotypes, were tested for their in vivo effectiveness against grey mold of table grapes, resulting in two St. bacillaris ('N22_I1' and 'S13_I3'), one S. diversa ('N22_I3'), one A. pullulans ('OLB_9.1_VL') and one H. uvarum ('OLB_9.1_BR') yeast strains that were marked as efficient and good BCAs. Their mechanisms of action were characterized through in vitro assays, and additional characteristics were evaluated to assess the economic feasibility and viability for future technological employment. Their effectiveness was tested by reducing the working concentration, their antagonistic effect on a wide range of fungal pathogens, their ability to survive in formulations with long shelf life, and their safety to human health.

Tryptophol Improves the Biocontrol Efficacy of Scheffersomyces spartinae against the Gray Mold of Strawberries by Quorum Sensing

Previously, we reported that marine yeast Scheffersomyces spartinae exhibited biocontrol efficacy against the gray mold of strawberries caused by Botrytis cinerea. Herein, tryptophol, a quorum-sensing molecule, was identified in the metabolites of S. spartinae. Subsequently, we found that 25 μM tryptophol promoted population density, biofilm formation, and cell aggregation of S. spartinae. Furthermore, 25 μM tryptophol improved the biocontrol efficacy of S. spartinae against B. cinerea in vitro and in the strawberry fruit. Under a scanning electronic microscope, tryptophol facilitated colonization and biofilm formation on strawberry wounds, showing that tryptophol increased the biocontrol efficacy of S. spartinae via quorum sensing. Transcriptome analysis revealed that tryptophol upregulated the gene expression of SDS3, DAL81, DSE1, SNF5, SUN41, FLO8, and HOP1, which was associated with cell adhesion or biofilm formation. Thus, to the best of our knowledge, this study was the first to report that tryptophol improved the biocontrol efficacy of S. spartinae via quorum sensing.

Composition and variability of core phyllosphere fungal mycobiota on field-grown broccoli

BACKGROUND

Fresh vegetables harbor an assemblage of different microorganisms on their surfaces. The phyllosphere microbiota is important for maintaining plant health and managing crop quality before and after harvest. However, the diversity and ecology of fungal communities are largely unexplored in fresh vegetables. This study investigated the phyllosphere mycobiota of field-grown broccoli florets (n = 66) collected from 22 farms across four regions in Korea, using culturing, amplicon sequencing of the internal transcribed spacer region, and microbial network analysis.

RESULTS

Microbial network analysis identified core genera (Purpureocillium, Filobasidium, Cystofilobasidium, Papiliotrema, Aureobasidium, and unclassified genera of Capnodiales) specific to the broccoli phyllosphere. The composition and network complexity of core and unique populations varied among farming regions, and was associated with local agro-meteorological conditions. The complexity of microbial associations was higher in mature communities than in immature communities, but complexity was lost upon development of plant pathogenic disease. Broccoli mycobiota were classified according to the dominance of Purpurecillium. While Purpurecillium-type microbiota were prevalent in normal samples, Filobasidium-type microbiota were frequently observed in immature, damaged, or postharvest samples.

CONCLUSIONS

Together, fungal communities were important components of phyllosphere microbiota on fresh vegetables, and have substantial potential for exploitation to enhance and stabilize plant health and growth.

Effectiveness of a Phage Cocktail as a Potential Biocontrol Agent against Saprophytic Bacteria in Ready-To-Eat Plant-Based Food

This study aimed to evaluate the effectiveness of the phage cocktail to improve the microbiological quality of five different mixed-leaf salads: rucola, mixed-leaf salad with carrot, mixed-leaf salad with beetroot, washed and unwashed spinach, during storage in refrigerated conditions. Enterobacterales rods constituted a significant group of bacteria in the tested products. Selected bacteria were tested for antibiotic resistance profiles and then used to search for specific bacteriophages. Forty-three phages targeting bacteria dominant in mixed-leaf salads were isolated from sewage. Their titer was determined, and lytic activity was assessed using the Bioscreen C Pro automated growth analyzer. Two methods of phage cocktail application including spraying, and an absorption pad were effective for rucola, mixed leaf salad with carrot, and mixed leaf salad with beetroot. The maximum reduction level after 48 h of incubation reached 99.9% compared to the control sample. In washed and unwashed spinach, attempts to reduce the number of microorganisms did not bring the desired effect. The decrease in bacteria count in the lettuce mixes depended on the composition of the autochthonous saprophytic bacteria species. Both phage cocktail application methods effectively improved the microbiological quality of minimally processed products. Whole-spectral phage cocktail application may constitute an alternative food microbiological quality improvement method without affecting food properties.

Specific Microbial Communities Are Selected in Minimally-Processed Fruit and Vegetables according to the Type of Product

Fruits and vegetables (F&V) products are recommended for the daily diet due to their low caloric content, high amount of vitamins, minerals and fiber. Furthermore, these foods are a source of various phytochemical compounds, such as polyphenols, flavonoids and sterols, exerting antioxidant activity. Despite the benefits derived from eating raw F&V, the quality and safety of these products may represent a source of concern, since they can be quickly spoiled and have a very short shelf-life. Moreover, they may be a vehicle of pathogenic microorganisms. This study aims to evaluate the bacterial and fungal populations in F&V products (i.e., iceberg lettuces, arugula, spinaches, fennels, tomatoes and pears) by using culture-dependent microbiological analysis and high-throughput sequencing (HTS), in order to decipher the microbial populations that characterize minimally-processed F&V. Our results show that F&V harbor diverse and product-specific bacterial and fungal communities, with vegetables leaf morphology and type of edible fraction of fruits exerting the highest influence. In addition, we observed that several alterative (e.g., Pseudomonas and Aspergillus) and potentially pathogenic taxa (such as Staphylococcus and Cladosporium) are present, thus emphasizing the need for novel product-specific strategies to control the microbial composition of F&V and extend their shelf-life.

Microbial volatile organic compounds: Antifungal mechanisms, applications, and challenges

The fungal decay of fresh fruits and vegetables annually generates substantial global economic losses. The utilization of conventional synthetic fungicides is damaging to the environment and human health. Recently, the biological control of post-harvest fruit and vegetable diseases via antagonistic microorganisms has become an attractive possible substitution for synthetic fungicides. Numerous studies have confirmed the potential of volatile organic compounds (VOCs) for post-harvest disease management. Moreover, VOC emission is a predominant antifungal mechanism of antagonistic microorganisms. As such, it is of great significance to discuss and explore the antifungal mechanisms of microbial VOCs for commercial application. This review summarizes the main sources of microbial VOCs in the post-harvest treatment and control of fruit and vegetable diseases. Recent advances in the elucidation of antifungal VOC mechanisms are emphasized, and the applications of VOCs produced from antagonistic microorganisms are described. Finally, the current prospects and challenges associated with microbial VOCs are considered.

Application Potential of Bacterial Volatile Organic Compounds in the Control of Root-Knot Nematodes

Plant-parasitic nematodes (PPNs) constitute the most damaging group of plant pathogens. Plant infections by root-knot nematodes (RKNs) alone could cause approximately 5% of global crop loss. Conventionally, chemical-based methods are used to control PPNs at the expense of the environment and human health. Accordingly, the development of eco-friendly and safer methods has been urged to supplement or replace chemical-based methods for the control of RKNs. Using microorganisms or their metabolites as biological control agents (BCAs) is a promising approach to controlling RKNs. Among the metabolites, volatile organic compounds (VOCs) have gained increasing attention because of their potential in the control of not only RKNs but also other plant pathogens, such as insects, fungi, and bacteria. This review discusses the biology of RKNs as well as the status of various control strategies. The discovery of VOCs emitted by bacteria from various environmental sources and their application potential as BCAs in controlling RKNs are specifically addressed.

Combination of chitosan coating and heat shock treatments to maintain postharvest quality and alleviate cracking of Akebia trifoliate fruit during cold storage

Akebia trifoliata fruit cracks easily, which shortens the shelf life and declines commercial value. This work aimed to evaluate the effects of heat shock and coating treatments on postharvest quality of A. trifoliata fruit and to elucidate the mechanism underlying retarding cracking by cell wall metabolism. Coating could decline cracking incidence (from 16.05% to 3.61%), decay incidence (from 31.21% to 18.06%), total soluble solids (TSS), and malondialdehyde (MDA) content compared to uncoated treatment during 35 days of storage. Heat shock could further decrease decay incidence but did not influence TSS, pH, firmness, and starch. Heat shock at 40 °C combined with coating treatment had the best preservation performance with the highest synthetic score (4.41). Furthermore, coated fruit displayed lower β-glucosidase and polygalacturonase activities which resulted in higher cellulose and Na₂CO₃-soluble pectin. These modifications together with lower weight loss, MDA, and ion leakage contributed to the lower cracking incidence.

Anti-Fungal Analysis of Bacillus subtilis DL76 on Conidiation, Appressorium Formation, Growth, Multiple Stress Response, and Pathogenicity in Magnaporthe oryzae

In recent years, biological control has gained more attention as a promising method to combat plant disease. Such severe diseases cited include rice blasts caused by Magnaporthe oryzae. However, more effective microbial strains with strong adaptability still need to be identified. Therefore, we sought to assess the conidia germination, and formation of appressorium of DL76 in Magnaporthe oryzae. Besides, we also aimed at understanding the growth, multiple stress response and pathogenicity in Magnaporthe oryzae. We isolated Bacillus subtilis DL76 from a rice farm, which observed a strong antimicrobial effect on M. oryzae. The sterilized culture filtrate of DL76 inhibited the growth of M. oryzae, which motivated us to deduce the influence of DL76 on the pathogenicity of M. oryzae. We screened the effect of Bacillus subtilis DL76 on M. oryzae guy11. It demonstrated that sterilized culture filtrate (1 × 10⁷ CFU/mL) of DL76 can delay and even suppress the germination of conidia and (1 × 10⁷ and 1 × 10⁶ CFU/mL) prevent the formation of appressorium in vitro and in vivo. DL76 became hypersensitive to osmotic, oxidative, and cell wall degrading agents. In addition, the relative transcript levels of stress-responsive genes oxidative and osmotic were down-regulated by DL76 except for sod1, cat1, and cat2. In vivo assessment of the antifungal activity of Bacillus subtilis using conidia suspension of DL76 reduced the incidence and severity of rice blast. Conclusively, our results show that DL76 is essential for controlling rice blast by inhibiting conidiation, growth, multiple stress tolerance, and pathogenicity in M. oryzae.

The Effect of Lactiplantibacillus plantarum BX62 Alone or in Combination with Chitosan on the Qualitative Characteristics of Fresh-Cut Apples during Cold Storage

In order to explore whether beneficial lactic acid bacteria (LAB) could prolong the shelf life and improve the quality of fresh-cut apples, Lactiplantibacillus plantarum BX62, which was isolated from traditional fermented yak yogurt, and chitosan (CT), were applied to fresh-cut apples, subsequently stored at 4 °C. On days 0, 2, 4, 6, and 8, apple slices were taken for physicochemical, microbiological analysis, and sensory evaluation. The results showed that apple slices coated with L. plantarum BX62 (8 log CFU/mL) presented lower weight loss and browning rate, higher DPPH scavenging capacity, and achieved more effective inhibition of polyphenol oxidase (PPO) and peroxidase (POD) activities compared to the control samples. The application of CT alone or in combination with L. plantarum BX62 resulted in a significant reduction in aerobic mesophilic bacteria (AMB), aerobic psychrophilic bacterial (APB), yeast and molds (YAMs) counts (2.31 log CFU/g for AMB, 2.55 for APB, and 1.58 for YAMs). In addition, L. plantarum BX62 coated apples showed acceptable sensory properties in terms of color, flavor, taste, texture, and overall visual quality during 8 d of storage. On this basis, L. plantarum BX62 could be used as an excellent bio-preservative to extend the shelf life and improve the quality of fresh-cut apples.

Development and Characterization of Yeast-Incorporated Antimicrobial Cellulose Biofilms for Edible Food Packaging Application

The unique properties and advantages of edible films over conventional food packaging have led the way to their extensive exploration in recent years. Moreover, the incorporation of bioactive components during their production has further enhanced the intrinsic features of packaging materials. This study was aimed to develop edible and bioactive food packaging films comprising yeast incorporated into bacterial cellulose (BC) in conjunction with carboxymethyl cellulose (CMC) and glycerol (Gly) to extend the shelf life of packaged food materials. First, yeast biomass and BC hydrogels were produced by Meyerozyma guilliermondii (MT502203.1) and Gluconacetobacter xylinus (ATCC53582), respectively, and then the films were developed ex situ by mixing 30 wt.% CMC, 30 wt.% Gly, 2 wt.% yeast dry biomass, and 2 wt.% BC slurry. FE-SEM observation showed the successful incorporation of Gly and yeast into the fibrous cellulose matrix. FTIR spectroscopy confirmed the development of composite films through chemical interaction between BC, CMC, Gly, and yeast. The developed BC/CMC/Gly/yeast composite films showed high water solubility (42.86%). The yeast-incorporated films showed antimicrobial activities against three microbial strains, including Escherichia coli, Pseudomonas aeruginosa, and Saccharomyces aureus, by producing clear inhibition zones of 16 mm, 10 mm, and 15 mm, respectively, after 24 h. Moreover, the films were non-toxic against NIH-3T3 fibroblast cells. Finally, the coating of oranges and tomatoes with BC/CMC/Gly/yeast composites enhanced the shelf life at different storage temperatures. The BC/CMC/Gly/yeast composite film-coated oranges and tomatoes demonstrated acceptable sensory features such as odor and color, not only at 6 °C but also at room temperature and further elevated temperatures at 30 °C and 40 °C for up to two weeks. The findings of this study indicate that the developed BC/CMC/Gly/yeast composite films could be used as edible packaging material with high nutritional value and distinctive properties related to the film component, which would provide protection to foods and extend their shelf life, and thus could find applications in the food industry.

Application of Processing and Packaging Hurdles for Fresh-Cut Fruits and Vegetables Preservation

Recently, consumers' demand for fresh, nutritious, and convenient food has shown a significant rise. This trend has forced increased sales of minimally processed and/or pre-packed fruit- and vegetable-based products. New product development and the diversification of plant-based foods have supported this growth. The food production sector should balance this requirement with the necessity to provide safe food with extended shelf life while meeting consumer demands for novel, nutritious, and affordable food products. The use of alternative "soft hurdles" may result in a decrease in the rate of food deterioration and spoilage attributed to microbial activity or other physiological/chemical degradation reactions. The objective of the article is to provide a systematic review of the preservative effect of the available hurdles implemented during processing and packaging of fresh-cut fruits and vegetables, focusing on recent applications aiming at improving product quality and prolonging their limited shelf life.

Screening of Lactic Acid Bacteria for the Bio-Control of Botrytis cinerea and the Potential of Lactiplantibacillus plantarum for Eco-Friendly Preservation of Fresh-Cut Kiwifruit

Botrytis cinerea, responsible for grey mold, represents the first biological cause of fruit and vegetable spoilage phenomena in post-harvest. Kiwifruit is a climacteric fruit particularly prone to this mold infestation during storage. Lactic acid bacteria (LAB) are food-grade bacteria that can synthesize several metabolites with antimicrobial activity and are, therefore, suggested as promising and eco-friendly resources for the bio-control of molds on fruits and vegetables. In this work, we propose the screening of a collection of 300 LAB previously isolated from traditional sourdoughs for their ability to counteract in vitro the growth of Botrytis cinerea CECT 20973. Only 2% of tested LAB strains belonging to Lactiplantibacillus plantarum species, exerted a strong antagonism against B. cinerea. The cell-free supernatants were partially characterized and results clearly indicated that high levels of lactic acid contributed to the antagonistic activity. PAN01 and UFG 121 cell-free supernatants were investigated as potential bio-control agents in a preliminary in vivo assay using freshly cut kiwifruits as a food model. The application of cell-free supernatants allowed to delay the growth of B. cinerea on artificially contaminated kiwifruits until two weeks. The antagonistic activity was greatly affected by the storage temperature (25 °C and 4 °C) selected for the processed fruits, suggesting the importance to include microbial-based solution in a broader framework of hurdle technologies.

Native Vineyard Non-Saccharomyces Yeasts Used for Biological Control of Botrytis cinerea in Stored Table Grape

Postharvest spoilage fungi, such as Botrytis cinerea, are considered the main cause of losses of fresh fruit quality and vegetables during storage, distribution, and consumption. The current control strategy is the use of SO₂ generator pads whose application is now largely under observation. A high quantity of SO₂ can be deleterious for fresh fruits and vegetables and it is not allowed in organic agriculture. For this reason, great attention has been recently focused on identifying Biological Control Agents (BCA) to implement biological approaches devoid of chemicals. In this direction, we carried out our study in isolating five different non-Saccharomyces yeast strains from local vineyards in the South of Italy as possible BCA. We performed both in vitro and in vivo assays in semi-commercial conditions on detached grape berries stored at 0 °C, simulating the temperature normally used during cold storage, and obtained relevant results. We isolated three M. pulcherrima strains and one L. thermotolerans strain able to largely antagonize the development of the B. cinerea, at both in vitro and in vivo conditions. In particular, we detected the ability of the three isolates of M. pulcherrima strains Ale4, N20/006, and Pr7 and the L. thermotolerans strain N10 to completely inhibit (100% in reduction) the mycelial growth of B. cinerea by producing fungistatic compounds. We found, using an extracellular lytic enzymes activity assay, that such activity could be related to lipid hydrolyzation, β-1,3-glucanase and pectinase activity, and pectinase and protease activity, depending on the yeasts used. Results from our in vitro assays allowed us to hypothesize for M. pulcherrima strains Ale4 and N20/006 a possible combination of both the production of soluble metabolites and volatile organic compounds to antagonize against B. cinerea growth. Moreover, in semi-commercial conditions, the M. pulcherrima strain N20/006 and L. thermotolerans strain N10 showed relevant antagonistic effect also at low concentrations (with a significantly reduction of ‘slip skin’ incidence of 86.4% and 72.7%, respectively), thus highlighting a peculiar property to use in commercial development for organic agriculture and the handling process.

Maintaining Physicochemical, Microbiological, and Sensory Quality of Pineapple Juice (Ananas comosus, Var. ‘Queen Victoria’) through Mild Heat Treatment

Shelf life of freshly prepared pineapple juice is short and requires refrigerated conditions of storage. Mild heat treatment remains the easiest way to prolong juice shelf life for small companies. This study was constructed to assess pineapple cv. Queen Victoria juice shelf life from a broad examination of its quality and to propose the most appropriate thermal treatment to increase shelf life without any perceptible decrease in quality. From 25 independent batches of pineapple, collected in different areas and seasons from Reunion Island, the variability of juice physicochemical and microbiological quality was determined. Juice pH values were the highest for fruit harvested in summer, but the juice acidity remained low enough to prevent pathogen spore-forming bacteria growth. During storage at 4 °C, color was modified, and yeasts and molds were the main microbial group exhibiting growth. Assessment of sensory quality resulted in the proposal of a shelf life comprising between three and seven days. Compared to higher temperatures, heat treatment at 60 °C was enough to ensure a good microbiological quality for 30 days, but sensory characteristics and color changes led to the proposal of a shelf life of seven days for pineapple juice treated at 60 °C.

Suppression of Rice Blast by Bacterial Strains Isolated from Cultivated Soda Saline-Sodic Soils

Rice blast caused by Magnaporthe oryzae is one of the most serious rice diseases worldwide. Biological control is gaining popularity as a promising method for the control of this disease; however, more effective microbial strains with strong adaptability in rice fields need to be identified. Here, we report for the first time the successful identification of biocontrol bacterial strains from frozen soils of the soda saline-sodic land. We isolated 82 bacterial strains from rice fields in the western Songnen Plain of China, one of the three major soda saline soils in the world. Five of the isolated strains exhibited strong inhibition to M. oryzae growth. The potential strains were identified as Bacillus safensis JLS5, Pseudomonas koreensis JLS8, Pseudomonas saponiphila JLS10, Stenotrophomonas rhizophila JLS11 and Bacillus tequilensis JLS12, respectively, by 16s RNA gene sequence analysis. The antagonistic assay and the artificial inoculation tests showed that JLS5 and JLS12 could effectively inhibit conidial germination and pathogenicity of the rice blast fungus, both preventively and curatively. The suppression of pathogenicity was further confirmed by greenhouse experiments, showing the effectiveness of JLS5 and JLS12 as a potential biological control agents of M. oryzae. The potential application of these cold-tolerant strains for rice blast control in cold regions is discussed. Our data suggest that soda saline-sodic soils are a rich source for biocontrol strain isolation.

Lactic Acid Bacteria as Antibacterial Agents to Extend the Shelf Life of Fresh and Minimally Processed Fruits and Vegetables: Quality and Safety Aspects

Eating fresh fruits and vegetables is, undoubtedly, a healthy habit that should be adopted by everyone (particularly due to the nutrients and functional properties of fruits and vegetables). However, at the same time, due to their production in the external environment, there is an increased risk of their being infected with various pathogenic microorganisms, some of which cause serious foodborne illnesses. In order to preserve and distribute safe, raw, and minimally processed fruits and vegetables, many strategies have been proposed, including bioprotection. The use of lactic acid bacteria in raw and minimally processed fruits and vegetables helps to better maintain their quality by extending their shelf life, causing a significant reduction and inhibition of the action of important foodborne pathogens. The antibacterial effect of lactic acid bacteria is attributed to its ability to produce antimicrobial compounds, including bacteriocins, with strong competitive action against many microorganisms. The use of bacteriocins, both separately and in combination with edible coatings, is considered a very promising approach for microbiological quality, and safety for postharvest storage of raw and minimally processed fruits and vegetables. Therefore, the purpose of the review is to discuss the biopreservation of fresh fruits and vegetables through the use of lactic acid bacteria as a green and safe technique.

Changes of Quality of Minimally-Processed Pineapple (Ananas comosus, var. 'Queen Victoria') during Cold Storage: Fungi in the Leading Role

Minimally-processed pineapple stored under refrigerated conditions is highly perishable. We aimed to characterize the evolution of physicochemical, sensory and microbiological quality during cold storage. Pineapple batches were sampled from several locations in Reunion Island and then minimally processed. In the processing step, the variability of firmness and counts of yeasts and molds were observed. Moreover, correlations between the sampling season and pH and b* color component, as well as between fungal population and b* parameter were observed. During storage, the visual aspect of pineapple cuts changed to brown and shiny, whereas olfactive descriptors shifted from fruity descriptors and fresh to fermented, alcoholic and milky. The values for pH, TA and TSS did not significantly vary according to storage time. A decrease in firmness and C* color parameter was observed. Yeast and mold counts were significantly higher after 7 days of storage. The diversity in yeasts and molds was mainly dependent on the considered batches observed from PCR-DGGE profiles. Fungal species were isolated from spoiled pineapple cuts. The implication of Penicilllium citrtrinum, Talaromyces amestolkiae, Rhodotorula mucilaginosa, Saccharomyces cerevisiae, and Meyerozyma caribbica in the spoilage of minimally-processed pineapple cuts was further demonstrated.